This invention relates to a transmission for and a method of changing speed and torque from an input power source. More particularly, the invention relates to a transmission for and a method of selecting from an "infinite" number of output torques and speeds, from maximum to as low as zero output speed, for vehicles, industrial speed changers, and the like, wherein ripple, or variation in rotational speed induced by crank action, is removed from the output.
Numerous devices and methods have been devised to change the speed and torque from a prime mover. One category of such devices and methods involves variable and fixed speed transmissions known as ratchet drives. Transmissions of this type include those that contain variable throw cranks, variably displaced fulcrums, and variable length lever arms.
An example of a variable throw system is described in U.S. Pat. No. 3,915,129 by Rust. In this device, a timing cam, with a distance from axis of rotation to cam surface that varies along its axis of rotation, is used to vary valve operating characteristics as a function of the position of a cam follower along the axis of rotation of the cam. Examples of other such devices have been described in U.S. Pat. No. 3,915,129; U.S. Pat. No. 3,229,546; U.S. Pat. No. 2,159,739; Italian Pat. No. 460047; and French Pat. No. 590,087.
Transmissions usually have fixed gear ratios that, although suitable for many uses, may be inadequate when the speed or torque needed is not efficiently provided by available gear ratios. For example, if the lowest gear ratio provided by a transmission having certain fixed gear ratios does not provide sufficiently low speed or sufficiently high torque for a given application, then the transmission is not suitable for the job. Thus it would be advantageous to provide a transmission that can furnish an infinite number of gear ratios and, consequently, an infinite number of output speeds and torques, between zero and some maximum.
Another problem associated with many transmissions is that shifting between gear ratios involves loss of power. Shifting gears while driving a motorized vehicle uphill illustrates this problem, inasmuch as the loss of power associated with shifting gears rapidly results in a loss of momentum. Thus, it would be advantageous to provide a transmission that could be shifted between an infinite number of available gear ratios without interrupting output power.
Additionally, many industrial machines are powered by constant speed electrical motors. Thus, it would be desirable to provide an industrial speed changer that can provide a wide variety of output speeds and torques. Because of the large variety of uses for such speed changers, it would be desirable to have a family of industrial speed changers that could fit the many needs for them, yet that could be manufactured from a few identical parts.
Certain applications require wide ranges in transmission gear ratios, such as in certain types of bicycles. Since a human does not generate much power except at certain pedaling speeds, it would be advantageous to provide a transmission that, efficiently furnishes a wide range of selectable gear ratios to allow for increased speed and distance for the same or less effort.
It would also be advantageous to provide a transmission that is inexpensive to build, yet reliable. Such a transmission would be suitable for many different kinds of vehicles, from bicycles to motorized vehicles such as cars, trucks, buses, trains, tractors, and the like.
Also, a transmission that is light in weight and has a wide range of transmission ratios would not only provide improved fuel economy, but also improved acceleration and hill climbing ability.